1. Field of the Invention
The present invention relates to data storage systems with capability to store data upon different types of storage media, such as disk drive storage, magnetic tape storage, and other varieties. More particularly, the data storage system of this invention responds to data storage requests by automatically analyzing the data to be stored, and then selecting the optimal type of output media according to factors such as the data size, the type of output media installed in the system, the availability of different output media types, and the urgency of the storage request.
2. Description of the Related Art
With the increasing importance of electronic information today, there is a similar increase in the importance of reliable data storage. The market abounds with different means of data storage today, ranging from minuscule integrated circuits to giant tape storage facilities that can occupy an entire room. Many data storage systems utilize several different types of storage in order to reap the particular benefit of each different type of storage. In implementation, data storage is often separated into several different levels, each level exhibiting a different data access time or data storage cost.
A first, or highest level of data storage involves electronic memory, usually dynamic or static random access memory (DRAM or SRAM). Electronic memories take the form of semiconductor integrated circuits where millions of bytes of data can be stored on each circuit, with access to such bytes of data measured in nanoseconds. The electronic memory provides the fastest access to data since access is entirely electronic.
A second level of data storage usually involves direct access storage devices (DASD). DASD storage, for example, includes magnetic and/or optical disks. Data bits are stored as micrometer-sized magnetically or optically altered spots on a disk surface, representing the xe2x80x9conesxe2x80x9d and xe2x80x9czerosxe2x80x9d that comprise the binary value of the data bits. Magnetic DASD includes one or more disks that are coated with remnant magnetic material. The disks are rotatably mounted within a protected environment. Each disk is divided into many concentric tracks, or closely spaced circles. The data is stored serially, bit by bit, along each track. An access mechanism, known as a head disk assembly (HDA) typically includes one or more read/write heads, and is provided in each DASD for moving across the tracks to transfer the data to and from the surface of the disks as the disks are rotated past the read/write heads. DASDs can store Gigabytes of data, and the access to such data is typically measured in milliseconds (orders of magnitudes slower than electronic memory). Access to data stored on DASD is slower than electronic memory due to the need to physically position the disk and HDA to the desired data storage location.
A third or lower level of data storage includes tapes, tape libraries, and optical disk libraries. Access to library data is much slower than electronic or DASD storage because a robot is necessary to select and load the needed data storage medium. Also, in the case of tape storage, access may be slowed by the need to serially position the tape media. An advantage of these storage systems is the reduced cost for very large data storage capabilities, on the order of Terabytes of data. Tape storage is often used for backup purposes. That is, data stored at the higher levels of data storage hierarchy is reproduced for safe keeping on magnetic tape. Access to data stored on tape and/or in a library is presently on the order of seconds.
As mentioned above, many data storage systems incorporate numerous output media types in order to reap the distinct benefits of each type. With so many different output media types in one system, however, it can be challenging to choose the appropriate media type for each particular storage operation.
One known approach accumulates all data sets in DASD storage, and later during a defined window, moves data sets to tape. While this approach offers the advantage of moving all the data congruently together, it also requires data to be moved twice, first onto DASD and later onto tape. Also, this approach does not take advantage of tape""s typically faster throughput for the original storage operation, and does not consider the possibility that larger data sets may not be stored at all if DASD does not have enough remaining free space. Another design option is to default to using a certain media type, but allow other types to be specified by command. The disadvantage of using this technique is that it relies on end users to decide where to route storage requests, regardless of whether such users are qualified to make such technical decisions. And, depending upon the number and arrival rate of data storage requests, it may be difficult or even impossible for a human operator to select the appropriate output media type for each storage request. Moreover, using a human operator to choose the output media type for each storage request incurs labor costs and also delays the speed of data storage.
Consequently, numerous challenges face those attempting to satisfy data storage requests in storage systems with multiple output media types.
Broadly, the present invention concerns a data storage system with multiple output media types, where requests to store data objects are automatically analyzed to aid in selecting the optimal output media types. In choosing the output media type best suited to quickly and efficiently complete each storage request, the storage system considers (1) attributes of the data object itself, such as its size, (2) any perceived urgency required to complete the storage request, and (3) attributes and conditions of the system""s storage devices, such as the availability of different output media types, presence of other storage requests queued for storage for each type, level of ongoing access of each storage type by concurrent storage tasks, delays to initiate storage such as mount/demount times, amount of storage space in different output media types, and the like.
In one particular implementation of this approach, the system utilizes tape and DASD as the output media types. A storage manager component of the system runs a storage analysis/management program, which analyzes each request to store a data object. Depending upon the system""s configuration, storage requests may arise from customer applications, or from internal processes such as migration of data from one storage site to another. If the data storage request is not urgent, the storage manager opts to use tape. For urgent storage requests, the storage manager tempers its choice according to the data object""s size. For large data objects, the storage manager chooses tape. For small data objects, the storage manager uses DASD unless either of the following special conditions applies, in which case the storage manager utilizes tape: (1) one of the tape drives contains a mounted, non-busy tape that is already allocated to serve the storage analysis/management program, and no large or medium-sized data objects await storage, or (2) the DASD is already being accessed by its maximum number of concurrent tasks, there is a non-busy tape drive accessible to the storage analysis/management program, and a tape is ready to conduct input/output (I/O) before the DASD. The relative readiness of tape and DASD to conduct I/O may be considered predictively (by estimation), or in real time (by waiting to see which media is ready first). For medium-sized data objects, the storage manager chooses tape unless the following special conditions apply, in which case the storage manager uses DASD: (1) all tape drives accessible to the storage analysis/management program are busy, or (2) the DASD is being accessed by less than its maximum number of concurrent tasks, and there are no small-sized data objects queued for storage.
The foregoing features may be implemented in a number of different forms. For example, the invention may be implemented to provide a method of analyzing requests to store data objects to select the optimal output media type. In another embodiment, the invention may be implemented to provide an apparatus such as a data storage system configured as described herein to analyze requests to store data objects in order to select the optimal output media type. In still another embodiment, the invention may be implemented to provide a signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital data processing apparatus to analyze requests to store data objects in order to select the optimal output media type. Another embodiment concerns logic circuitry having multiple interconnected electrically conductive elements configured to analyze requests to store data objects in order to select the optimal output media type.
The invention affords its users with a number of distinct advantages. Importantly, the invention completes data storage requests as quickly as possible by selecting the optimal output media type. Data storage requests complete more quickly because, as analyzed by the invention, the selected media type has earlier readiness, greater size, or other beneficial properties to efficiently satisfy the data storage request. Also, the pre-storage analysis of this invention reduces the likelihood of data storage requests ultimately failing due to lack of free space in a particular output media type, or for other such reasons. As another advantage, the invention can quickly select the output media type for each data storage request because the invention utilizes computer-driven machinery instead of requiring a human operator to manually make such decisions. And, for this same reason, the invention can consider a greater number and complexity of factors in selecting the optimal type of output media, with less likelihood of error. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.